Conventional methods for forming low density boron carbide cermet have not been notably successful. The ball milling method, one of the oldest approaches, requires that: the concentrated refractory ore be refined to a pure oxide or other chemical compound; this compound be reduced to pure refractory metal and ground into a powder; the refractory metal be heated in the presence of carbon to form a metal carbide; the metal carbide be mixed with a powdered metal binder; the mixture be comminuted by ball milling to produce a slurry of blended cermet powder (of representative size 1-10 um diameter); and the slurry be dried and/or compacted to form a cermet powder. This process is expensive and labor-intensive, and it produces a cermet powder with density close to that of the metal binder, which is usually much heavier than the refractory metal or compound. For example, solid boron carbide has a maximum density of approximately 2.52 gm/cm.sup.3, whereas solid titanium has a density of approximately 4.5 gm/cm.sup.3. The higher density of the cermet is in part due to the small size particles of refractory material that are used in or result from such processes.
Borg, Lai, Riley and Wolfe, in U.S. Pat. No. 3,892,644, disclose a method of making very fine carbon cermet powders (typically, 0.01-0.1 um diameter), using a metal oxide and a metal carbide mixed with a polymerized furfuryl alchohol resin binder containing a catalyst, dried and formed as an anode for a high intensity electric arc circuit. The circuit is operated in a non-oxidizing atmosphere, and the anode is thereby consumed, producing a homogeneous cermet powder of finely divided metal carbide and metal binder particles.
An arc furnace process for producing boron carbide is disclosed by Scott in U.S. Pat. No. 3,161,471, using a reaction of boron oxide ore electrodes and coke or other pure carbon form positioned elsewhere in the furnace. This process produces small solid ingots of boron carbide. It is unclear whether a third (binder) element such as a metal could be added to the mixture.